The relationship between abundance of the lepidopteran borers Helicoverpa armigera Hubner and Maruca vitrata (Geyer) and damage and yield loss in short-duration pigeonpeas was studied in two multilocation trials in 1995–1996 and 1996–1997 rainy seasons at four locations in India: Patancheru (Andhra Pradesh), Akola (Maharashtra), Sardarkrishi Nagar (Gujarat) and Vamban (Tamil Nadu). Larval populations of Helicoverpa armigera (Hubner) and Maruca vitrata (Geyer) were correlated with pod damage and grain yields. Significant correlation of location, years and genotype on insect population, level of damage and grain yield was obtained. The effect of plant type on lepidopteran pod damage was also observed. The relationships between pod damage, yield and larval population of Helicoverpa and Maruca are discussed.

The effect of infestation of lepidopteran borers on yield of maize was assessed at three locations in the forest and forest/savanna transition zones of Cameroon, during the first and second season of 1992. Maize was treated once or twice with the systemic carbofuran at different developmental stages. The species encountered were the stem-boring noctuids Busseola fusca and Sesamia calamistis, which oviposit on and attack pre-tasseling stages of maize; the stem-boring pyralid Eldana saccharina, which attacks plants at and after tasseling; and two ear borers, namely the pyralid Mussidia nigrivenella and the tortricid Cryptophlebia leucotreta. Generally, carbofuran reduced infestations by B. fusca and S. calamistis but had little or no effect on species attacking the plant's later stages. Thus early treatments with granules into the whorl were more efficient than late treatments as a side dressing, and a second late treatment had little effect. During the first season, late-attacking species were predominant and grain yield losses of 17–44 % were found in one location only. During the second season, species attacking young plants (mainly B. fusca) became predominant in all three locations and yield losses of 30 to 41 % were found in two of the three locations. The percentage of ears with damage was especially high during the second season. As green maize is an important source of cash income in the area and damaged ears cannot be sold, the economic loss was likely considerable.

The economic injury level (EIL) of the maize stem borer, Chilo partellus (Swinhoe) was determined by artificially infesting maize (cv. Katumani) plants at three different growth stages; viz, 20, 40 and 60 days old plants with varying densities of newly hatched larvae; viz, 2, 4, 6, 8, 10 and 12 per plant constituting the borer population. The grain yield data obtained from the infested and the protected plants showed that maximum yield reduction and stalk damage occurred to the 20-day old crop, while there was insignificant larval effect on yields for the 60-day old crop. Regression analyses gave a significant linear equation (y = a + bx) which estimated the yields per plant at different infestation levels and these were used to calculate the economic injury level at each stage. The resultant EIL was 3.2 and 3.9 larvae/plant for 20- and 40-day old plants, respectively.

Varietal differences with respect to yield losses due to whitefly, Bemisia tabaci Genn. attack were observed at the “sooty-mould level” and “economic threshold (ET) level” of infestation. At the peak infestation level leading to sooty-mould development, the losses varied from 21.7 to 31.8% in boll numbers, 10.3 and 23.7% in boll-weight; 25.9 and 48.9% in seed cotton yield; 12.4 and 153% in seed oil and 29.4 and 66.5% in seed germination among the group of promising new cultures viz., LK 861, LPS 141 and L 389 and other group of commonly cultivated varieties viz., JKHY 1, MCU 5 and ADB 10050, respectively. Besides, the fibre qualities like length, strength, fineness and maturity were also found to be adversely affected.